Method of manufacturing pixel electrode for reflection type display device

ABSTRACT

A process of a pixel electrode of a direct-sight type of reflection type liquid-crystal display device is simplified. A pixel electrode 120 of a reflection type liquid-crystal display device is formed of an aluminum film which is formed by sputtering. In forming the aluminum film, moisture is intentionally contained in atmosphere, and also a sample is heated. With this process, aluminum grains grow so that irregularities of μm order is formed on the surface of the aluminum film. The aluminum film thus formed allows the incident light to be irregularly reflected so that it is in a visually white muddy state. This is suitable to the pixel electrode for the reflection type liquid-crystal display device.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a technique for forming anelectrode used for a pixel electrode of a reflection type liquid-crystaldisplay, and more particularly to a method of manufacturing a pixelelectrode for a direct-sight type of reflection type liquid-crystaldisplay.

[0003] 2. Description of the Related Art

[0004] The reflection type liquid-crystal display has a function ofconducting display with the combination of reflection of a lightinputted from the exterior by a pixel electrode with optical modulationaction of liquid crystal.

[0005] The reflection type liquid-crystal display is roughly classifiedinto a direct sight type and a projection type. In the direct sighttype, the pixel electrode is required to irregularly reflect a light tobe reflected by the electrode so that it is seen that the reflectedlight is white-muddy. On the other hand, in the projection type, thepixel electrode is required to be finished into a mirror surface.

[0006] In the reflection type liquid-crystal display device, either of astate in which an incident light is reflected by the pixel electrode andoutputted to the exterior of the device, or a state in which theincident light is not outputted to the exterior of the device isselectively obtained in each cell by utilizing the optical modulationaction of the liquid crystal, thereby conducting a bright or darkdisplay in each cell, and images are displayed in combination with thebright cells and dark cells.

[0007] In the direct-sight type liquid-crystal display, the incidentlight from the exterior is reflected by the pixel electrode and thenoutputted to the exterior of the device, i.e., which is the brightdisplay. However, since the display is obtained by reflecting theincident light by the pixel electrode as is reflected by a mirrorwithout any changes, there occurs such a phenomenon that the display isglittered or darkened depending on an angle of view. That is, thereoccurs a phenomenon that the angle of view is narrowed.

[0008] This is caused by a fact that the reflection state of theincident light is different according to the angle of view. In order toeliminate this problem, the pixel electrode needs to be devised so thatthe incident light is irregularly reflected. With the device that allowsirregular reflection, the pixel electrode appears to be in a visuallywhite muddy state (it is needless to say that in the case where specialprocessing is conducted on the pixel electrode so that only a light of aspecific wavelength is inputted to the pixel electrode, the pixelelectrode is not always white-muddy).

[0009] In general, in a direct-sight type display device, the surface ofa pixel electrode is subjected to light etching to form irregularitiesthereon, to thereby cause the above-mentioned irregular reflection.

[0010] It is a supreme demand to suppress the manufacture costs as muchas possible for the direct-sight type of reflection type liquid-crystaldisplay. This is because that since the direct-sight type of reflectiontype liquid-crystal display device requires no back light which isdifferent from the transmission type, it facilitates a low powerconsumption and a weight-lighting. As a result, the direct-sight type ofreflection type liquid crystal display is mainly used for a cheapdisplay unit of an information processing terminal or a portabletelephone.

[0011] Under the above circumstances, an important problem resides inreducing its manufacturing process as much as possible to suppress theproduction costs as much as possible.

[0012] A process of forming irregularities on the surface of the abovepixel electrode through etching is so complicated that wet etching ordry etching is required in a final stage.

[0013] In particular, since this etching is conducted after most of thedevice is completed, the use of wet etching suffers from a problem thatetchant enters the interior of the device. Also, the use of dry etchingsuffers from electrostatic breakdown, etc., which are caused by theapplication of a bias voltage. In particular, the structure of theactive matrix type is employed, those problems become more serious.

[0014] In order to evade those problems, such a trouble-some labor asmaking a process management standard more strict is required. However,this makes the manufacture costs increase.

SUMMARY OF THE INVENTION

[0015] The present invention has been made in view of the aboveproblems, and therefore an object of the present invention is to providea means for obtaining a structure where an incident light is irregularlyreflected on the surface of a pixel electrode through a simpler method.

[0016] In order to solve the above problems, according to one aspect ofthe present invention, there is provided a method of manufacturing apixel electrode for a reflection type display device having a structurein which an incident light is reflected, characterized by comprising thesteps of:

[0017] forming grains on the surface of a film made of aluminum ormainly contains aluminum when forming the film; and

[0018] forming a surface from which the incident light is irregularlyreflected.

[0019] According to another aspect of the present invention, there isprovided a method of manufacturing a pixel electrode for a reflectiontype display device having a structure in which an incident light isreflected, characterized by comprising the steps of:

[0020] forming a film made of aluminum or mainly contains aluminumthrough sputtering in which moisture is intentionally introduced; and

[0021] forming a surface from which the incident light is irregularlyreflected on the surface of the film.

[0022] According to still another aspect of the present invention, thereis provided a method of manufacturing a pixel electrode for a reflectiontype display device having a structure in which an incident light isreflected, characterized by comprising the steps of:

[0023] forming on a substrate having a heated insulating surface a filmmade of aluminum or mainly contains aluminum through sputtering in whichmoisture is intentionally introduced;

[0024] depositing aluminum grains simultaneously with the formation ofthe film, on the surface of the film made of aluminum or mainly containsaluminum; and

[0025] forming the surface from which the incident light is irregularlyreflected on the surface of the film.

[0026] According to yet still another aspect of the present invention,there is provided a method of manufacturing a pixel electrode for areflection type display device having a structure in which an incidentlight is reflected, wherein the pixel electrode is made of aluminum ormainly contains aluminum,

[0027] the method characterized by comprising the steps of:

[0028] when forming the pixel electrode made of aluminum or mainlycontains aluminum, heating a substrate and sputtering the pixelelectrode in which moisture is intentionally introduced; and

[0029] forming a film made of aluminum or mainly contains aluminumhaving a surface by which the incident light is irregularly reflected.

[0030] According to yet still another aspect of the present invention,there is provided a method of manufacturing a pixel electrode for areflection type display device having a structure in which an incidentlight is reflected, wherein the pixel electrode is made of aluminum ormainly contains aluminum,

[0031] the method characterized by comprising the steps of:

[0032] when forming the pixel electrode made of aluminum or mainlycontains aluminum, heating a substrate and sputtering the pixelelectrode in which moisture is intentionally introduced;

[0033] depositing aluminum grains simultaneously with the formation ofthe pixel electrode, on the surface of a film mad of aluminum or mainlycontains aluminum; and

[0034] forming a film made of aluminum or mainly contains aluminumhaving a surface by which the incident light is irregularly reflected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIGS. 1A to 1D are diagrams partially showing a process ofmanufacturing a reflection type active matrix liquid-crystal displayunit of the first embodiment;

[0036]FIG. 2 is a graph representing data of measured irregularities ofthe surface of an aluminum film as obtained in the first embodiment; and

[0037]FIGS. 3A to 3C are schematic diagrams showing electronicequipments each having a direct sight type display unit using pixelelectrodes of the present invention, respectively, in the thirdembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] A pixel electrode for a reflection type liquid-crystal displaydevice is manufactured using a material made of aluminum or mainlycontaining aluminum by sputtering. At this time, moisture is containedin an atmosphere. Preferably, a substrate (base substance) is heated.With this process, aluminum grains (having a grain diameter of nearlyseveral μm or less) are deposited, and the surface of an aluminum filmas obtained has irregularities as shown in FIG. 2.

[0039] This film enables intentional introduction of moisture to bereadily executed during the normal sputtering process.

[0040] Also, the diameter of the deposited aluminum grain and thedeposition state can be controlled according to the introduced amount ofmoisture or a heat temperature.

[0041] The aluminum film thus obtained allows an incident light to beirregularly reflected, thereby being capable of obtaining a visuallywhite-muddy state. Such films described above is suitable for the pixelelectrode for the reflection type liquid-crystal display device.

[0042] The simplest method of introducing moisture is a method in whichmoisture is introduced in an atmosphere. In particular, as one of thesimplest method, there is a method of introducing moisture using air.Also, there can be applied a method of containing moisture in a target.

[0043] It is considered that the action of moisture promotes theformation of grains because oxygen exists in the deposition of thealuminum film, so that the deposition of grains is progressed. Also,heating has an effect to promote the growth of grains.

[0044] The specific condition may be that air of about 0.1 to 5% ismixed with the sputtering atmosphere if air is used, for example, forintroduction of moisture.

[0045] Also, the temperature of heating may be selected from about 100to 300° C.

[0046] It should be noted that a material for forming an electrode maybe a material containing impurities or a material made of an alloyconsisting of aluminum and other metal material, other than the materialpurely containing aluminum.

First Embodiment

[0047] A first embodiment is directed to a process of manufacturing areflection type active matrix liquid-crystal display device. FIGS. 1A to1D are diagrams showing the process of manufacturing a reflection typeactive matrix liquid-crystal display unit according to this embodiment.

[0048] First, a silicon oxide film 102 is formed in thickness of 3000 Åon a glass substrate 101 as a base film by the plasma CVD method or thesputtering method.

[0049] Then, an amorphous silicon film not shown is formed on thesilicon oxide film 102, and also a laser light is irradiated onto theamorphous silicon such that the amorphous silicon film is changed into acrystalline silicon film. The crystalline silicon film thus obtained ispatterned to obtain an active layer 103.

[0050] Thus, a state shown in FIG. 1A is obtained. Subsequently, analuminum film not shown for formation of a gate electrode is formed inthickness of 4000 Å on the active layer 103 by the sputtering method.Then, a silicon nitride film 106 is formed in thickness of 1000 Å on thealuminum film by the plasma CVD method.

[0051] Thus, a state shown in FIG. 1B is obtained. Subsequently, ananodic oxide 108 is formed on side surfaces of the aluminum patternthrough the anodic oxidation. In this process, an electrolyte comes incontact with only the side surfaces of the aluminum pattern due to theexistence of the silicon nitride film 106 so that the anodic oxide 108selectively grows in a-direction of the side surfaces of the aluminumpattern.

[0052] Thus, an aluminum pattern 107 that functions as the gateelectrode is obtained as shown in FIG. 1C. In this state, doping ofimpurities that give one conductivity is conducted through the plasmadoping method. In this example, doping of P (phosphorus) is conducted tomanufacture an n-channel thin-film transistor.

[0053] In this doping process, a source region 109 and a drain region113 are formed in a self-alignment manner.

[0054] In this example, regions 110 and 112 are formed intohigh-resistant regions which are called offset gate regions. Also, aregion 111 is formed into a channel region.

[0055] Thus, a state shown in FIG. 1C is obtained. Thereafter, a siliconnitride film 114 is formed in thickness of 2000 Å as a first interlayerinsulating film by the plasma CVD method, and also a polyimide resinfilm 115 is formed on the silicon nitride film 114.

[0056] Subsequently, contact holes are formed to form a source electrode(a part of a source line) 116 and a drain electrode 117 which are formedof a multilayer film consisting of a titanium film, an aluminum film anda titanium film.

[0057] Thereafter, a polyimide resin film 118 is formed as a secondinterlayer insulating film on the polyimide resin film 115, and thenafter contact holes are formed, an aluminum film is formed in thicknessof 3000 Å by the sputtering method.

[0058] Conditions under which the films are formed are stated below.

[0059] target: aluminum target containing scandium of 0.18 wt % therein

[0060] film forming pressure: 0.26 Pa

[0061] RF power: 2000 W (13.56 MHz)

[0062] film thickness: 3000 Å

[0063] film forming time: 9.36 minutes

[0064] In this example, an argon gas containing air of 1% with humidityof 50% is employed as a sputtering gas. During sputtering, a substrateis heated at 150° C. by a resistant heating heater.

[0065] A sputtering device as used is a normal high-frequency magnetrontype sputtering device to which a gas supply system is added.

[0066] In the case where the aluminum film is formed by the sputteringas in this embodiment, aluminum grains are deposited so that the surfaceof the aluminum film as obtained has irregularities. Then, an incidentlight is irregularly reflected on the rough surface of the aluminum filmso that a white-muddy state can be obtained.

[0067] After the aluminum film is obtained, it is patterned to obtainpixel electrode patterns 119 and 120. In this example, the pattern 120is formed into a pixel electrode which is connected to a drain of thethin-film transistor shown. Further, the pattern 119 is a pixelelectrode pattern on the left side in the figure.

[0068] A result of measuring the state of the surface of the pixelelectrode made of aluminum thus obtained through a surfaceirregularities tester is shown in FIG. 2. The principle of the surfaceroughness tester is that a probe scans the surface of a sample so thatthe irregularities of the surface of the sample is detected as a finemovement of the probe and converted into an electric signal, thusmeasuring the irregularities of the surface of the sample.

[0069] As is apparent from FIG. 2, the surface of the aluminum film thusobtained has proper irregularities to obtain a visually uniformwhite-muddy state in relation to the rough surface. Such an aluminumfilm is ideal as the pixel electrode for the direct-sight typeliquid-crystal display unit.

[0070] It should be noted that although this embodiment is directed to acase where a top-gate type thin-film transistor is used, a thin-filmtransistor of another type such as a bottom gate type can be used.

[0071] Also, since the importance of the present invention resides inthe method of forming the pixel electrode, the present inventiondisclosed herein may be applied to a simple matrix type instead of theactive matrix type as described in this embodiment.

[0072] Further, the kinds of liquid crystal employed in theliquid-crystal display unit may be a TN type, an STN type, aferro-electricity type, a diffusion type, a guest host type or the like.

Second Embodiment

[0073] A second embodiment is directed to an example in which conditionsin forming an aluminum film that constitutes the pixel electrodedescribed in the first embodiment are changed. In this embodiment, steamis contained in the sputtering atmosphere.

Third Embodiment

[0074] A third embodiment is directed to an example of an electronicdevice (applied products) having a direct-sight type display unit towhich the present invention is applied, which is shown in FIGS. 3A to3C. It should be noted that the electronic device means a product onwhich a semiconductor circuit and/or an electro-optic device is mounted.

[0075] The electronic devices to which the present invention are appliedare a video camera, an electronic still camera, a car navigation, aportable information terminal (mobile computer, a portable telephone, aPHS (a personal handy phone system), etc), a personal computer or thelike.

[0076]FIG. 3A shows a portable telephone which is made up of a mainbody, 2001, a voice output section 2002, a voice input section 2003, adirect-sight type display unit 2004, an operation switch 2005, and anantenna 2006. The display unit 2004 includes the pixel electrodes of thepresent invention.

[0077]FIG. 3B shows a video camera which is made up of a main body 2101,a direct-sight type display unit 2102, a voice input section 2103, anoperation switch 2104, a battery 2105, and an image receiver 2106. Thepresent invention can be applied to the display unit 2102.

[0078]FIG. 3C shows a mobile computer which is made up of a main body2201, a camera section 2202, an image receiver 2203, an operation switch2204 and a direct-sight type display unit 2205. The present invention isapplicable to the display unit 2205.

[0079] Using the pixel electrodes of the present invention, thoseelectronic devices, more particularly the portable information devicecan be provided inexpensively.

[0080] With application of the present invention disclosed herein, astructure where the incident light is irregularly reflected on thesurface of the pixel electrode can be obtained in the simpler manner.Also, the present invention can provide the technique by which thedirect-sight type of reflection type liquid-crystal display unit can beobtained at the lower costs.

[0081] The present specification describes examples in which the presentinvention is employed mainly to the reflection type active matrixliquid-crystal display unit. However, the present invention described inthe present specification is not limited by or to only the appliedscope, but can be applied to the manufacture of the electrode which isapplied to another use of irregular reflection of the incident light.

What is claimed is:
 1. A method of manufacturing an electronic devicecomprising at least a reflection type display device, said methodcomprising the steps of: forming at least a thin film transistor on aninsulating surface, said thin film transistor including a source region,a drain region and a channel region between the source and drainregions; forming a first interlayer insulating film covering the thinfilm transistor; forming a second interlayer insulating film comprisingan organic material over the first interlayer insulating film; forming afilm comprising aluminum by sputtering with moisture intentionallyinduced; forming a pixel electrode by patterning the film comprisingaluminum, said pixel electrode being on the second interlayer insulatingfilm and being electrically connected with the drain region of the thinfilm transistor, wherein an incident light is reflected on the pixelelectrode.
 2. A method according to claim 1 , wherein the firstinterlayer insulating film comprises a silicon nitride film.
 3. A methodaccording to claim 1 , wherein the second interlayer insulating filmcomprises a polyimide resin film.
 4. A method according to claim 1 ,wherein the electronic device is one selected from the group consistingof a video camera, an electronic still camera, a car navigation, apersonal computer, a portable information terminal such as a mobilecomputer, a portable telephone, a PHS (personal handy phone system). 5.A method according to claim 1 , wherein the thin film transistor is oneselected from the group consisting of a top gate type thin filmtransistor and a bottom gate type thin film transistor.
 6. A method ofmanufacturing an electronic device comprising at least a reflection typedisplay device, said method comprising the steps of: forming at least athin film transistor on an insulating surface, said thin film transistorincluding a source region, a drain region and a channel region betweenthe source and drain regions; forming a first interlayer insulating filmcovering the thin film transistor; forming a first organic resin film onthe first interlayer insulating film; forming a source electrode on thefirst organic resin film, said source electrode being connected with thesource region of the thin film transistor; forming a drain electrode onthe first organic resin film, said drain electrode being connected withthe drain region of the thin film transistor; forming a second organicresin film on the first organic resin film; forming a film comprisingaluminum by sputtering with moisture intentionally induced; forming apixel electrode by patterning the film comprising aluminum, said pixelelectrode being on the second interlayer insulating film and beingelectrically connected with the drain electrode, wherein an incidentlight is reflected on the pixel electrode.
 7. A method according toclaim 6 , wherein the first interlayer insulating film comprises asilicon nitride film.
 8. A method according to claim 6 , wherein each ofthe second organic resin films comprise a polyimide resin film.
 9. Adevice according to claim 6 , wherein the electronic device is oneselected from the group consisting of a video camera, an electronicstill camera, a car navigation, a personal computer, a portableinformation terminal such as a mobile computer, a portable telephone, aPHS (personal handy phone system).
 10. A device according to claim 6 ,wherein the thin film transistor is one selected from the groupconsisting of a top gate type thin film transistor and a bottom gatetype thin film transistor.
 11. A method of manufacturing an electronicdevice comprising at least a reflection type display device, said methodcomprising the step of: forming a pixel electrode comprising aluminumover an insulating surface by sputtering with moisture intentionallyinduced, wherein an incident light is reflected on the pixel electrode.12. A method according to claim 11 , further comprising the step of:forming at least a thin film transistor being formed over the insulatingsurface, wherein the thin film transistor including a source region, adrain region and a channel region between the source and drain regions,wherein the thin film transistor is one selected from the groupconsisting of a top gate type thin film transistor and a bottom gatetype thin film transistor.
 13. A device according to claim 11 , whereinthe electronic device is one selected from the group consisting of avideo camera, an electronic still camera, a car navigation, a personalcomputer, a portable information terminal such as a mobile computer, aportable telephone, and a personal handy phone system.